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Poster Presentation 3-18
Limits for Alkaline Detoxification of Dilute Acid Hydrolysates
Nils-Olof Nilvebrant1, Anders Reimann1, Filipe de Sousa1 and Leif J. Jönsson2
1STFI Swedish Pulp and Paper Research Institute P.O. Box 5604, SE-114 86, Stockholm, Sweden
2Biochemistry Division for Chemistry, Karlstad University SE-651 88, Karlstad, Sweden
Telephone: +4686767134; Fax: +468104380; Email: non@stfi.se
In addition to fermentable sugars, dilute acid hydrolysates of lignocellulose contain compounds that inhibit fermenting microorganisms, such as Saccharomyces cerevisiae. Previous results show that phenolic compounds and furan aldehydes, and to some extent aliphatic acids, act as inhibitors in dilute acid hydrolysates of spruce. Treatment of lignocellulose hydrolysates with alkali, usually in the form of overliming to pH 10, has been frequently employed as a detoxification method to improve the fermentability. Overliming, or addition of calcium hydroxide, has been found to be more efficient as a detoxification method than the addition of sodium hydroxide. The effect of alkali treatment under different conditions on the concentrations of sugars and inhibitors was tested in model experiments with glucose as well as in an authentic spruce hydrolysate.
Already at pH 9, more than 20 % of the glucose was lost in a dilute acid hydrolysate of spruce performed at 80°C for 1 hour. In a factorial design experiment with the hydrolysate, sodium hydroxide was used to raise and maintain the pH, using a pH-control unit. The other variables, temperature and time, were changed simultaneously. The concentrations of the different monosaccharides were analyzed. The changes in the concentrations of furan aldehydes and phenols were also determined. Aliphatic acids are end products from alkaline degradation of monosaccharides and their concentrations were monitored.
The degradation of glucose proceeded considerably slower than that of xylose. The difference between sodium and calcium hydroxide was compared under selected conditions. The use of calcium hydroxide resulted in more substantial sugar degradation than for sodium hydroxide. This could be attributed to the catalytic effect of calcium ions on the enolization reaction, which may influence both the kinetics of the following benzilic acid rearrangement and the product pattern.
In conclusion, the conditions used for detoxification with alkali should be carefully controlled to optimize the positive effects and minimize the degradation of fermentable sugars.
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